Re: [PATCH v4 3/4] can: kvaser_usb: Add support for the Usbcan-II family

Hi!

On Mon, Jan 12, 2015 at 02:53:02PM +0100, Olivier Sobrie wrote:

Hello,

On Sun, Jan 11, 2015 at 03:36:12PM -0500, Ahmed S. Darwish wrote:

quoted

From: Ahmed S. Darwish <redacted>

...

quoted

@@ -98,7 +128,13 @@
 #define CMD_START_CHIP_REPLY		27
 #define CMD_STOP_CHIP			28
 #define CMD_STOP_CHIP_REPLY		29
-#define CMD_GET_CARD_INFO2		32
+#define CMD_READ_CLOCK			30
+#define CMD_READ_CLOCK_REPLY		31

These two defines are not used.

They were added for completeness: the only gap in our continuous
sequence of command IDs from 12 to 39 ;-) No big deal, to be
removed in the next submission.

...

quoted

+
+struct kvaser_msg_tx_acknowledge_header {
+	u8 channel;
+	u8 tid;
+};

Is this struct really needed? Can't you simply use
leaf_msg_tx_acknowledge or usbcan_msg_tx_acknowledge
structures to read the header.
Same for kvaser_msg_rx_can_header.

They're added to ensure type-safety throughout the code. Basically
they're the common part of a command that has different wire format
between the Leaf and the USBCan, but share a common header.  Such
notation was only added when it was strictly necessary.

For example, there are three functions where 'rx_can_header' is
referenced in the driver, and one function where 'tx_acknowledge_header'
is referenced. Without such header structure, I'll have to sprinkle
3 to 4 extra blocks of:

	switch (dev->family) {
	       case KVASER_LEAF: 
	       case KVASER_USBCAN:
	}

which would be _really_ ugly. The *_header notation ensures that, in
the body of each function, we're accessing the fields in a very safe
manner.

Thanks,
Darwish